Configuring operating parameters of  a medical device based on a type of source of a disruptive energy field

ABSTRACT

An implantable medical device (IMD) configures one or more operating parameters of the IMD based on a type of source of a disruptive energy field to which the IMD is exposed. The disruptive energy field may, in one example, include magnetic and/or radio frequency (RF) fields generated by an MRI scanner. In one aspect, the IMD may distinguish between different types of MRI scanners and select an exposure operating mode tailored to reduce the effects of the particular type of MRI scanner. In another aspect, the IMD may adjust one or more operating parameters that will be used when the IMD returns to a normal operating mode after exposure to the MRI scanner based on the type of MRI scanner to which the IMD is exposed.

This application claims priority from U.S. Provisional Application No.61/256,342, filed Oct. 30, 2009, the entire content of which isincorporated herein by reference.

TECHNICAL FIELD

The disclosure relates generally to implantable medical devices and, inparticular, to the configuration of operating parameters of animplantable medical device (IMD)based on a type of source of adisruptive energy field to which the IMD is exposed.

BACKGROUND

A wide variety of IMDs that deliver a therapy to and/or monitor aphysiologic condition of a patient have been clinically implanted orproposed for clinical implantation in patients. IMDs may deliver therapyor monitor conditions with respect to a variety of organs, nerves,muscles or tissues of the patients, such as the heart, brain, stomach,spinal cord, pelvic floor or the like. In some cases, IMDs may deliverelectrical stimulation therapy via one or more electrodes, which may beincluded as part of one or more elongated implantable medical leads.

For example, an implantable cardiac device, such as a cardiac pacemakeror implantable cardioverter-defibrillator, provides therapeuticstimulation to the heart by delivering electrical therapy signals suchas pulses or shocks for pacing, cardioversion, or defibrillation viaelectrodes of one or more implantable leads. As another example, aneurostimulator may deliver electrical therapy signals, such as pulses,to a spinal cord, brain, pelvic floor or the like, to alleviate pain ortreat symptoms of any of a number of neurological or other diseases,such as epilepsy, gastroparesis, Alzheimer's, depression, obesity,incontinence and the like.

Exposure of the IMD to a disruptive energy field may result inundesirable operation of the IMD. The IMD may be exposed to thedisruptive energy field for any of a number of reasons. For example, oneor more medical procedures may need to be performed on the patientwithin whom the IMD is implanted for purposes of diagnostics or therapy.For example, the patient may need to have a magnetic resonance imaging(MRI) scan, computed tomography (CT) scan, electrocautery, diathermy orother medical procedure that produces a magnetic field, electromagneticfield, electric field or other disruptive energy field.

The disruptive energy field may induce energy on one or more of theimplantable leads coupled to the IMD or directly on one or morecomponents of the IMD. The IMD may inappropriately detect the inducedenergy on the leads as physiological signals. Alternatively, oradditionally, the induced energy on the leads may result in theinability to correctly detect physiological signals. In either case,detection of the induced energy on the leads as physiological signalsmay result in the IMD delivering therapy when it is not desired orwithholding therapy when it is desired. In other instances, the inducedenergy on the leads or on the components of the IMD may result ininadvertent stimulation or heating of the tissue and/or nerve siteadjacent to the electrodes of the leads or adjacent to the housing ofthe IMD. Such heating may compromise pacing and sensing thresholds atthe site, which could result in reduced therapy efficacy.

SUMMARY

In general, this disclosure relates to configuration of operatingparameters of an implantable medical device (IMD) based on a type ofsource of a disruptive energy field to which the IMD is exposed. Thedisruptive energy field may, in one example, include magnetic and/orradio frequency (RF) fields generated by an MRI scanner. Although thetechniques of this disclosure are described in the context of disruptiveenergy fields generated by an MRI scanner, the techniques may be used tocontrol operation of the IMD within environments in which other types ofdisruptive energy fields of other sources are present.

The IMD is configured into an exposure operating mode prior to or uponexposure to the disruptive energy field. The exposure operating modecauses the IMD to operate in a manner that accounts for the presence ofstrong disruptive energy fields. In accordance with the techniques ofthis disclosure, the IMD may distinguish different types of disruptivefield sources based on one or more detected conditions and configureoperating parameters of the IMD based on the type of disruptive fieldsource detected. In one aspect, the IMD may distinguish betweendifferent types of MRI scanners and select a first exposure operatingmode for a first type of MRI scanner (e.g., a 1.5 Tesla (1.5 T) MRIscanner) and select a second exposure operating mode for a second typeof MRI scanner (e.g., a 3.0 Tesla (3.0 T) MRI scanner). The operatingparameters of each of the exposure operating modes may be tailored toreduce the effects of the different MRI scanners, which producedifferent magnetic fields and RF field frequencies.

In another aspect, the IMD may adjust one or more operating parametersthat will be used when the IMD returns to a normal operating mode basedon the type of disruptive field source. For example, the IMD may adjustthe one or more operating parameters of the normal operating mode by afirst amount when exposed to a first type of MRI scanner (e.g., a 1.5 TMRI scanner) and adjust the one or more operating parameters by a secondamount when exposed to a second type of MRI scanner (e.g., a 3.0 T MRIscanner). The one or more parameters of the normal operating mode thatare adjusted based on the type of MRI scanner may include a pacingamplitude, a pacing pulse width, and/or a sensitivity of a senseamplifier. The adjustment of the one or more parameters for use in thenormal operating mode after exposure to the MRI scanner may be inaddition to or instead of selecting different exposure operating modes.

In one example, this disclosure is directed to an implantable medicaldevice comprising a memory to store operating parameters for a pluralityof exposure operating modes, wherein each of the plurality of exposureoperating modes corresponds to a particular type of magnetic resonanceimagining (MRI) scanner, and a processor to detect a conditionindicative of a presence of an MRI scanner, determine a type of MRIscanner in response to detecting the condition, retrieve from the memorythe operating parameters of the one of the plurality of exposureoperating modes corresponding to the determined type of MRI scanner, andconfigure the implantable medical device to operate in accordance withthe retrieved operating parameters.

In another example, this disclosure is directed to a method comprisingdetecting a condition indicative of a presence of a magnetic resonanceimaging (MRI) scanner, determining a type of MRI scanner in response todetecting the condition, selecting one of a plurality of exposureoperating modes based on the determination of the type of MRI scanner,wherein each of the plurality of exposure operating modes corresponds tooperating parameters for use during exposure to a particular type of MRIscanner, and configuring the implantable medical device to operate inaccordance with the operating parameters of the selected exposureoperating mode.

In a further example, this disclosure is directed to an implantablemedical device comprising means for storing a plurality of exposureoperating modes, wherein each of the plurality of exposure operatingmodes corresponds to operating parameters for use during exposure to aparticular type of a magnetic resonance imaging (MRI) scanner, means fordetecting a condition indicative of a presence of MRI scanner, means fordetermining a type of MRI scanner in response to detecting thecondition, means for selecting one of the plurality of exposureoperating modes based on the determination of the type of MRI scanner,and means for configuring the implantable medical device to operate inaccordance with the operating parameters of the selected exposureoperating mode.

This summary is intended to provide an overview of the subject matterdescribed in this disclosure. It is not intended to provide an exclusiveor exhaustive explanation of the techniques as described in detailwithin the accompanying drawings and description below. Further detailsof one or more examples are set forth in the accompanying drawings andthe description below. Other features, objects, and advantages will beapparent from the description and drawings, and from the statementsprovided below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a conceptual diagram illustrating an environment in which animplantable medical device (IMD) is exposed to a disruptive energyfield.

FIG. 2 is a conceptual diagram illustrating an example medical systemthat may be used to provide therapy to patient.

FIG. 3 is a functional block diagram of an example configuration ofcomponents of an IMD.

FIG. 4 is a functional block diagram illustrating some of the componentsof the IMD of FIG. 3 in further detail.

FIG. 5 is a functional block diagram illustrating example components forimplementing exposure operating modes tailored for specific types of MRIscanners.

FIG. 6 is a flow diagram illustrating an example operation of an IMDselecting an exposure operating mode based on the type of MRI scanner.

FIG. 7 is a flow diagram illustrating an example operation of an IMDdetecting the presence of an MRI scanner and determining the type of MRIscanner.

FIG. 8 is a flow diagram illustrating another example operation of anIMD detecting the presence of an MRI scanner and determining the type ofMRI scanner.

FIG. 9 is a flow diagram illustrating an example operation of an IMDadjusting one or more parameters of a normal operating mode based on thetype of MRI scanner.

DETAILED DESCRIPTION

FIG. 1 is a conceptual diagram illustrating an environment 10 in whichan implantable medical device (IMD) 14 is exposed to a disruptive energyfield 11. IMD 14 is implanted within patient 12 to provide therapy toand/or to monitor a physiological condition of patient 12. Thetechniques, however, are not limited to devices implanted within patient12. For example, the techniques may be used in conjunction with anexternal medical device that is adversely affected by disruptive energyfield 11.

IMD 14 may be any of a variety of devices that provide therapy topatient 12, monitor a condition of patient 12, or both. For example, IMD14 may be a device that provides electrical stimulation therapy via oneor more implantable leads that include one or more electrodes (not shownin FIG. 1). In some instances, IMD 14 may be a device that provideselectrical stimulation therapy in the form of cardiac rhythm managementtherapy to a heart of patient 12 via leads implanted within one or moreatria and/or ventricles of the heart. In other instances, IMD 14 may bea device that provides electrical stimulation to a tissue site ofpatient 12 proximate a muscle, organ or nerve, such as a tissueproximate a vagus nerve, spinal cord, brain, stomach, pelvic floor orthe like.

In addition to providing electrical stimulation therapy, IMD 14 maysense one or more physiological parameters of patient 12. When one ormore leads are implanted within the heart of patient 12, for example,electrodes of the leads may sense electrical signals attendant to thedepolarization and repolarizatoin of the heart to monitor a rhythm ofthe heart or detect particular heart conditions, e.g., tachycardia,bradycardia, fibrillation or the like. IMD 14 may sense a variety ofother physiologic parameters or other parameters related to a conditionof patient 12, including, for example, neurologic parameters,intracardiac or intravascular pressure, activity, posture, pH of bloodor other bodily fluids or the like. In some instances, IMD 14 may beused solely for monitoring a condition of patient 12. In other words,IMD 14 may not provide therapy to patient 12, but simply sense aphysiological or biological condition of patient 12.

In yet other instances, IMD 14 may be a device that delivers a drug ortherapeutic agent to patient 12, e.g., via a catheter. IMD 14 maydeliver, e.g., using a pump, the drug or therapeutic agent to a specificlocation of patient 12. IMD 14 may deliver the drug or therapeutic agentat a constant or variable flow rate. Drug pumps, infusion pump or drugdelivery devices may be used to treat symptoms of a number of differentconditions. For example, IMD 14 may deliver morphine or ziconotide toreduce or eliminate pain, baclofen to reduce or eliminate spasticity,chemotherapy to treat cancer, or any other drug or therapeutic agent(including saline, vitamins, etc.) to treat any other condition and/orsymptom of a condition.

Environment 10 includes an energy source or disruptive field source thatgenerates disruptive energy field 11 to which IMD 14 is exposed. In theexample illustrated in FIG. 1, the energy source or disruptive fieldsource is an MRI scanner 16. Although the techniques of this disclosureare described with respect to disruptive energy field 11 generated byMRI scanner 16, the techniques may be used to control operation of IMD14 within environments in which other types of disruptive energy fieldsare present. For example, IMD 14 may operate in accordance with thetechniques of this disclosure in environments in which disruptive energyfield 11 is generated by other sources, such as a CT scanner, X-raymachine, electrocautery device, diathermy device, ablation device,radiation therapy device, electrical therapy device, magnetic therapydevice, RFID security gate, or any other environment with devices thatradiate energy to produce magnetic, electromagnetic, electric fields orother disruptive energy fields.

MRI scanner 16 uses magnetic and radio frequency (RF) fields to produceimages of body structures for diagnosing injuries, diseases and/ordisorders. In particular, MRI scanner 16 generates a static magneticfield, gradient magnetic fields and/or RF fields. The static magneticfield is a non-varying magnetic field that is typically always presentaround MRI scanner 16 whether or not an MRI scan is in progress.Gradient magnetic fields are pulsed magnetic fields that are typicallyonly present while the MRI scan is in progress. RF fields are pulsed RFfields that are also typically only present while the MRI scan is inprogress. The magnitude, frequency or other characteristic of disruptiveenergy field 11 may vary based on the type of MRI scanner producing thefield.

Some or all of the various types of fields produced by MRI scanner 16may interfere with operation of IMD 14. In other words, one or more ofthe various types of fields produced by MRI scanner 16 may make updisruptive energy field 11. For example, the gradient magnetic and RFfields produced by MRI scanner 16 may induce energy on one or more ofthe implantable leads coupled to IMD 14. In some instances, IMD 14inappropriately detects the induced energy on the leads as physiologicalsignals, which may in turn cause IMD 14 to deliver undesired therapy orwithhold desired therapy. In other instances, the induced energy on theleads result in IMD 14 not detecting physiological signals that areactually present, which may again result in IMD 14 delivering undesiredtherapy or withholding desired therapy. The induced energy on the leadsor on the components of IMD 14 may be delivered to the tissue of patient12 resulting in inadvertent stimulation or heating of the tissueadjacent to electrodes of the leads or adjacent to the housing of IMD14. Such heating may compromise pacing and sensing thresholds at thesite, which could result in reduced therapy efficacy.

To reduce the undesirable effects of disruptive energy field 11, IMD 14is capable of operating in accordance with settings that are lesssusceptible to undesirable operation during exposure to disruptiveenergy field 11, referred to herein as the “exposure mode” or “exposureoperating mode.” In the case of an exposure operating mode thatspecifically accounts for MRI scans, the mode may be referred to as anMR Conditional mode or an MR Safe mode. Prior to being exposed or uponbeing exposed to disruptive energy field 11, IMD 14 is configured from anormal operating mode (e.g., the current operating mode) to the exposureoperating mode. IMD 14 may be automatically configured into the exposureoperating mode in response to detecting one or more conditionsindicative of the presence of MRI scanner 16.

As will be described in more detail below, IMD 14 may determine the typeof MRI scanner 16 to which IMD 14 is being exposed and adjust one ormore operating parameters of IMD 14 based on the type of MRI scanner 16.IMD 14 may, for example, determine the type of MRI scanner 16 based onone or more of a magnitude of a static and/or gradient magnetic field ora frequency of an RF field applied by the MRI scanner 16. In one aspectof this disclosure, IMD 14 may select an exposure operating mode that isspecifically tailored for the type of MRI scanner 16. In this manner,the exposure operating mode may be specifically tailored to reduce theeffects of the magnetic and RF fields of different magnitudes and/orfrequencies that correspond to the type of MRI scanner. In anotheraspect of this disclosure, IMD 14 may adjust one or more operatingparameters that will be used when IMD 14 returns to the normal operatingmode based on the type of MRI scanner 16. In this manner, IMD 14 mayadjust therapy or sensing to account for any effects caused by exposureto MRI scanner 16.

FIG. 2 is a conceptual diagram illustrating an example medical system 30that may be used to provide therapy to patient 12. Medical system 30includes an IMD 32 and leads 34 and 36 that extend from IMD 32. IMD 32may, for example, correspond to IMD 14 of FIG. 1. IMD 32 wirelesslycommunicates with programming device 18.

In the example illustrated in FIG. 2, IMD 32 is an implantable cardiacdevice that senses electrical activity of a heart 38 of patient 12and/or provides electrical stimulation therapy to heart 38 of patient12. The electrical stimulation therapy to heart 38, sometimes referredto as cardiac rhythm management therapy, may include pacing,cardioversion, defibrillation and/or cardiac resynchronization therapy(CRT). The combinations of cardiac therapies provided may be dependenton a condition of patient 12. In some instances, IMD 32 may provide notherapy to patient 12, but instead provide only sensing of electricalactivity or other variable of heart 38, such as in the case of animplantable loop recorder.

In the illustrated example, lead 34 is a right ventricular (RV) leadthat extends through one or more veins (not shown), the superior venacava (not shown), and right atrium 40, and into right ventricle 42 ofheart 38. Lead 34 includes electrodes 44 and 46 located along a distalend of lead 34. In the illustrated example, lead 36 is right atrial (RA)lead that extends through one or more veins and the superior vena cava,and into the right atrium 40 of heart 38. Lead 36 includes electrodes 50and 52 located along a distal end of lead 36.

Electrodes 44 and 50 may take the form of extendable helix tipelectrodes mounted retractably within an insulative electrode head (notshown) of respective leads 34 and 36. Electrodes 46 and 52 may take theform of ring electrodes. In other embodiments, electrodes 44, 46, 50 and52 may be other types of electrodes. For example, electrodes 44, 46, 50and 52 may all be ring electrodes located along the distal end of theassociated lead 34 or 36. Additionally, either or both of leads 34 and36 may include more than two electrodes or only a single electrode.

Each of the electrodes 44, 46, 50 and 52 may be electrically coupled toa respective conductor within the body of its associated lead 34 and 36.The respective conductors may extend from the distal end of the lead tothe proximal end of the lead and couple to circuitry of IMD 32. Forexample, leads 34 and 36 may be electrically coupled to a stimulationmodule, a sensing module, or other modules of IMD 32 via connector block54. In some examples, proximal ends of leads 34 and 36 may includeelectrical contacts that electrically couple to respective electricalcontacts within connector block 54. In addition, in some examples, leads34 and 36 may be mechanically coupled to connector block 54 with the aidof set screws, connection pins or another suitable mechanical couplingmechanism.

When IMD 32 is capable of delivering electrical stimulation therapy, IMD32 delivers the therapy (e.g., pacing pulses) to heart 38 via anycombination of electrodes 44, 46, 50 and 52 to cause depolarization ofcardiac tissue of heart 38. For example, IMD 32 may deliver bipolarpacing pulses to right atrium 40 via electrodes 50 and 52 of lead 36and/or may deliver bipolar pacing pulses to right ventricle 42 viaelectrodes 44 and 46 of lead 34. In another example, IMD 32 may deliverunipolar pacing pulses to atrium 40 and ventricle 42 using a housingelectrode (not shown) in conjunction with one of electrodes 44, 46, 50and 52. The housing electrode may be formed integrally with an outersurface of the hermetically-sealed housing of IMD 32 or otherwisecoupled to the housing. In some examples, the housing electrode isdefined by an uninsulated portion of an outward facing portion of thehousing of IMD 32.

Electrodes 44, 46, 50 and 52 may also sense electrical signals attendantto the depolarization and repolarization of heart 38. The electricalsignals are conducted to IMD 32 via one or more conductors of respectiveleads 34 and 36. IMD 32 may use any combinations of the electrodes 44,46, 50, 52 or the housing electrode for unipolar or bipolar sensing. Assuch, the configurations of electrodes used by IMD 32 for sensing andpacing may be unipolar or bipolar depending on the application. IMD 32may analyze the sensed signals to monitor a rhythm of heart 38 or detectan arrhythmia of heart 38, e.g., tachycardia, bradycardia, fibrillationor the like. In some instances, IMD 32 provides pacing pulses (or othertherapy) to heart 38 based on the cardiac signals sensed within heart38. In other words, pacing may be responsive to the sensed events.

As described above, exposure of IMD 32 to a disruptive energy field 11(FIG. 1) may result in undesirable operation. For example, gradientmagnetic and RF fields produced by MRI scanner 16 (FIG. 1) may induceenergy on one or more conductors of respective ones of implantable leads34 and 36 or on the housing electrode. In some instances, IMD 32inappropriately detects the induced energy on the conductors of leads 34or 36 as physiological signals, which may in turn cause IMD 32 todeliver undesired therapy or withhold desired therapy. In otherinstances, the induced energy on the conductors of leads 34 or 36 resultin IMD 32 not detecting physiological signals that are actually present,which may again result in IMD 32 delivering undesired therapy orwithholding desired therapy. In further instances, the induced energy onconductors of leads 34 or 36 or on components of IMD 32 results ininadvertent stimulation or heating of the tissue adjacent to electrodes44, 46, 50 and 52 or the housing of IMD 32. Such heating may compromisepacing and sensing thresholds at the site, which could result in reducedtherapy efficacy.

Configuring IMD 32 into an exposure operating mode may reduce, andpossibly eliminate, the undesirable effects that may be caused byexposure to disruptive energy field 11. As such, IMD 32 may beconfigured to operate in the exposure operating mode prior to orimmediately subsequent to entering the environment 10 in which thedisruptive energy field 11 is present, or prior to or immediatelysubsequent to the beginning of an MRI scan. In accordance with oneaspect of this disclosure, IMD 32 detects a condition indicative of apresence of an MRI scanner and determines a type of MRI scanner inresponse to detecting the condition. As will be described in furtherdetail below, IMD 32 may determine the type of MRI scanner based on thedetected condition, based on one or more other conditions or based onthe detected condition and one or more other conditions.

Based on the determination of the type of MRI scanner, IMD 32 adjustsone or more operating parameters of IMD 32. For example, IMD 32 mayselect the exposure operating mode corresponding to the particular typeof MRI scanner. In another example, IMD 32 may adjust one or moreoperating parameters to be used in the normal operating mode upon nolonger being exposed based on the type of MRI scanner.

A user, such as a physician, may interact with programming device 18 toconfigure one or more parameters of the plurality of exposure operatingmodes. For example, the user may specify a pacing mode (e.g.,atrial-based pacing mode, ventricular-based pacing mode or dual-chamberbased pacing mode), pacing amplitude, pacing pulse width, and/or pacingrate of the therapy energy delivered during the exposure operating mode.Typically, the pacing mode, pacing amplitude, pacing pulse width, andpacing rate of the therapy energy delivered during the exposureoperating mode will be the same regardless of the type of MRI scanner.However, in some instances, one or more of these settings may bedifferent based on the type of MRI scanner 16.

As another example, the user may specify filtering configurations to beused during each of the exposure operating modes. The user may, forexample, configure the exposure operating mode corresponding to a 1.5 TMRI scanner to implement a filter to attenuate signals at a firstfrequency (e.g., 64 MHz) and configure the exposure operating modecorresponding to a 3.0 T MRI scanner to implement a filter to attenuatesignals at a second frequency (e.g., 128 MHz). Programming device 18then transmits the selected settings of the one or more exposureoperating modes to IMD 32.

As a further example, the user may interact with programming device 18to configure one or more parameters for use in the normal operating modeafter being exposed to the MRI scanner. In some instances, theseparameters may differ based on the type of MRI scanner to which IMD 32is exposed. For example, the user may specify pacing parameters and/orsensing parameters to use during the normal operating mode after theexposure to MRI scanner 16 that may be different due to differentMRI-induced effects that may occur based on the type of MRI scanner 16.

The user may interact with a programming device 18 to communicate withIMD 32 for other purposes than configuring the exposure operating modeparameters. For example, the user may interact with programming device18 to retrieve physiological information, diagnostic information, logsof delivered therapies, or an assessment of the performance or integrityof IMD 32 or other components of medical system 30, such as leads or apower source of IMD 32. Programming device 18 may transmit acommunication requesting such information or receive the informationwithout providing such a request. The user may also interact withprogramming device 18 to program IMD 32, e.g., select values foroperational parameters of the normal operating mode of IMD 32, such as atherapy progression, an electrode or combination of electrodes of leads34 and 36 to use for delivering electrical stimulation (pulses orshocks), select parameters for the electrical pulse or shock (e.g.,pulse amplitude, pulse width, or pulse rate), select electrodes orsensors for use in detecting a physiological parameter of patient 12, orthe like.

Programming device 18 may communicate with IMD 32 via wirelesscommunication using any techniques known in the art. Examples ofcommunication techniques may include, for example, magnetic telemetry,low frequency telemetry, RF telemetry, tissue conductance telemetry (inwhich the body is used as a conductor), or acoustic telemetry, but othertechniques are also contemplated. In some instances, programming device18 and IMD 32 may communicate in the 402-405 MHz frequency band inaccordance with the Medical Implant Communications Service (MICS)frequency band regulation, in the 401-402 MHz or 405-406 MHz frequencybands in accordance with the Medical External Data Service (MEDS) bandregulations, in the unlicensed industrial, scientific and medical (ISM)band, or other frequency band.

Programming device 18 may be a dedicated hardware device with dedicatedsoftware for programming of IMD 32. Alternatively, programming device 18may be an off-the-shelf computing device running an application thatenables programming device 18 to program IMD 32. In some examples,programming device 18 may be a handheld computing device or a computerworkstation. Programming device 18 may, in some instances, include aprogramming head that may be placed proximate to the patient's body nearthe implant site of IMD 32 in order to improve the quality or securityof communication between IMD 32 and programming device 18. Programmingdevice 18 may include one or more processors, such as one or moremicroprocessors, digital signal processors (DSPs), application specificintegrated circuits (ASICs), field-programmable gate arrays (FPGAs),programmable logic circuitry, or the like, that may perform variousfunctions and operations, such as those described herein.

The configuration of medical system 30 illustrated in FIG. 2 is merelyan example. In other examples, medical system 30 may include more orfewer leads extending from IMD 32. For example, IMD 32 may be coupled tothree leads, e.g., a third lead implanted within a left ventricle ofheart 30. In another example, IMD 32 may be coupled to a single leadthat is implanted within either an atrium or ventricle of heart 38. Assuch, IMD 32 may be used for single chamber or multi-chamber cardiacrhythm management therapy.

In addition to more or fewer leads, each of the leads may include moreor fewer electrodes. In instances in which IMD 32 is used for therapyother than pacing, e.g., defibrillation or cardioversion, the leads mayinclude elongated electrodes, which may, in some instances, take theform of a coil. IMD 32 may deliver defibrillation or cardioversionshocks to heart 38 via any combination of the elongated electrodes andhousing electrode. As another example, medical system 30 may includeleads with a plurality of ring electrodes, e.g., as used in someimplantable neurostimulators.

In still other examples, a medical system may include epicardial leadsand/or patch electrodes instead of or in addition to the transvenousleads 34 and 36 illustrated in FIG. 2. Further, IMD 32 need not beimplanted within patient 12. In examples in which IMD 32 is notimplanted in patient 12, IMD 32 may deliver electrical stimulationtherapy to heart 38 via percutaneous leads that extend through the skinof patient 12 to a variety of positions within or outside of heart 38.

The techniques of this disclosure are described in the context ofcardiac rhythm management therapy for purposes of illustration. Thetechniques of this disclosure, however, may be used to operate an IMDthat provides other types of electrical stimulation therapy. Forexample, the IMD may be a device that provides electrical stimulation toa tissue site of patient 12 proximate a muscle, organ or nerve, such asa tissue proximate a vagus nerve, spinal cord, brain, stomach, pelvicfloor or the like. Moreover, the techniques may be used to operate anIMD that provides other types of therapy, such as drug delivery orinfusion therapies. As such, description of these techniques in thecontext of cardiac rhythm management therapy should not be limiting ofthe techniques as broadly described in this disclosure.

FIG. 3 is a functional block diagram of an example configuration ofcomponents of IMD 32. In the example illustrated by FIG. 3, IMD 32includes a control processor 60, sensing module 62, stimulation module66, disruptive field detector 68, telemetry module 70, memory 72 andpower source 74, all of which are interconnected by a data bus 76.

As described above, IMD 32 may detect a condition indicative of apresence of MRI scanner 16 and determine a type of MRI scanner inresponse to detecting the condition. Processor 60 of IMD 32 may receivea signal from disruptive field detector 68 and analyze the signal fromdisruptive field detector 68 to detect the condition indicative of thepresence of MRI scanner 16. In one example, disruptive field detector 68is a magnetic field detector that provides an output that varies as afunction of the magnitude of the magnetic field. Processor 60 mayanalyze the output of disruptive field detector 68 to determine thewhether the condition indicative of the presence of MRI scanner 16exists. In the case of the magnetic field detector, for example,processor 60 may determine whether the magnitude of the magnetic fieldexceeds a threshold.

In response to detecting the presence of MRI scanner 16, processor 60may determine the type of MRI scanner. Processor 60 may determine thetype of MRI scanner based on the signals used to detect the presence ofMRI scanner 16, based on one or more other signals or based on thesignals used to detect the presence of MRI scanner 16 and one or moreother conditions. For example, processor 60 may determine the type ofMRI scanner based on the signals from the magnetic field detector ofdisruptive field detector 68. Processor 60 may analyze these signals todetermine whether the magnitude corresponds with a 1.5 T MRI scanner ora 3.0 T MRI scanner. In instances in which the same signals are used todetect the presence and type of MRI scanner 16, processor 60 may beviewed as concurrently detecting the presence and type of MRI scanner16.

In another example, processor 60 determines the type of MRI scannerbased on at least one other signal. For instance, upon detecting thecondition indicative of the presence of the MRI scanner (e.g., magnitudeof magnetic field exceeds a threshold), processor 60 may determine afrequency of RF energy to determine the type of MRI scanner. Processor60 may determine that the MRI scanner is a 1.5 T scanner when thefrequency of RF energy is approximately 64 MHz and determine that theMRI scanner is a 3.0 T MRI scanner when the frequency of the RF energyis approximately 128 MHz. To this end, disruptive field detector 68 mayinclude an RF sensor comprising a stub, coil, or other structure thatoperates as an antenna to receive RF energy. In another example, asignal may be induced on antenna 78 by the pulsed RF fields generated byMRI scanner 16. In a further example, a signal may be induced on one ormore conductors within leads 34 or 36 by the pulsed RF fields generatedby MRI scanner 16.

In any case, processor 60 may analyze signals induced on disruptivefield detector 68, antenna 78 and/or conductors of leads 34 and 36 todetermine the frequency of the RF energy. Based on the frequency of theRF energy, processor 60 may determine the type of MRI scanner. In thisexample, processor 60 detects the presence of MRI scanner 16 in responseto detecting a first condition, e.g., the detection of a strong magneticfield, and determines the type of MRI scanner based on a secondcondition, e.g., the determined frequency of RF energy. Other techniquesmay be used to determine the presence of MRI scanner 16 and/or the typeof MRI scanner using any of a variety of conditions. The examples aboveare for example purposes only and should not be considered limiting ofthe techniques described in this disclosure.

Processor 60 may select an exposure operating mode corresponding to thetype of MRI scanner and enable the selected exposure operating modecorresponding to the type of MRI scanner upon determining the type ofMRI scanner. For example, processor 60 may select operating parametersof a first exposure operating mode when the type of MRI scanner is a 1.5T MRI scanner and select operating parameters of a second exposureoperating mode when the type of MRI scanner is a 3.0 T MRI scanner. Theselected exposure operating mode may include at least one operatingparameter that is specifically tailored for exposure to a particulartype of MRI scanner. For example, processor 60 may implement a filter toattenuate signals at a first frequency (e.g., 64 MHz) when operating inthe exposure operating mode corresponding to a 1.5 T MRI scanner andimplement a filter to attenuate signals at a second frequency (e.g., 128MHz) when operating in the exposure operating mode corresponding to a3.0 T MRI scanner.

Additionally or alternatively, processor 60 may control stimulationmodule 66 to deliver therapy having a different pacing amplitude and/orpulse width based on the type of MRI scanner. Thus, the pacing amplitudeand/or pulse width may be tailored for exposure to a specific type ofMRI scanner. For example, processor 60 may control stimulation module 66to adjust the pacing amplitude and/or pulse width by a first amount whenIMD 32 is exposed to a 1.5 T MRI scanner and adjust the pacing amplitudeand/or pulse width by a second amount when IMD 32 is exposed to a 3.0 TMRI scanner. The first amount may be larger than the second amount orsmaller than the second amount. In another aspect, the first amount orsecond amount may be equal to zero such that the pacing amplitude and/orpulse width are not adjusted for one type of MRI scanner, but adjustedfor another type of MRI scanner. In one instance, the adjustment may bean increase in pacing amplitude and/or pulse width.

In some instances, a number of the operating parameters of the exposureoperating modes corresponding to the different types of MRI scanners maybe the same. Continuing with the example above, the exposure operatingmodes of the 1.5 T and 3.0 T MRI scanners may have the same pacing mode,pacing amplitude, pacing pulse width, pacing rate, or other operatingparameter. As such, although each of the exposure operating modes mayinclude operating parameters specifically tailored for operation in aparticular MRI environment, e.g., specific filtering parameters, atleast some of the operating parameters of the exposure operating modesmay overlap.

As such, processor 60 may begin to operate in accordance with the commonexposure mode operating parameters prior to determining the type of MRIscanner and then enable the remaining operating parameters upondetermining the specific type of MRI scanner. For example, processor 60may operate in accordance with the common operating parameters (e.g.,pacing mode, pacing pulse amplitude, pacing pulse width, pacing rate, orthe like) upon detecting the presence of an MRI scanner and then enablethe operating parameters designed for a specific type of MRI scanner(e.g., implement a filter to attenuate RF signals of a particularfrequency) upon detecting the type of MRI scanner. In this manner, IMD32 may reduce the effect of any MRI scanner immediately upon exposure tothe MRI scanner and further reduce the effect of a particular type ofMRI scanner upon determining the type of MRI scanner.

In another example, processor 60 may operate in accordance with adefault exposure operating mode upon detecting the presence of an MRIscanner and then switch to the exposure operating mode corresponding tothe specific type of MRI scanner upon detecting the type of MRI scanner.The default exposure operating mode may correspond with an exposureoperating mode corresponding to the type of MRI scanner most frequentlyused, e.g., a 1.5 T MRI scanner. Alternatively, the default exposureoperating mode may be an exposure operating mode that includes thecommon parameters of the two or more exposure operating modes.

Processor 60 may automatically disable the exposure operating mode,e.g., in response to disruptive field detector 68 no longer detectingdisruptive energy field 11 of MRI scanner 16, after a predeterminedperiod of time (e.g., one hour), or other condition, or a combination oftwo or more conditions. In other words, processor 60 may automaticallyconfigure IMD 32 from the exposure operating mode back to the normaloperating mode based on the one or more conditions. In other instances,a user may manually disable the exposure operating mode of IMD 32, e.g.,via interaction with programming device 18. In other words, IMD 32 ismanually configured from the exposure operating mode to the normaloperating mode upon no longer being exposed to MRI scanner 16.

IMD 32 may use the determination of the type of MRI scanner to adjustone or more parameters that will be used when IMD 32 returns to thenormal operating mode upon no longer being exposed to MRI scanner 16. Inother words, IMD 32 may adjust one or more parameters of the normaloperating mode based on the type of MRI scanner. The adjustment of theone or more parameters of the normal operating mode for use afterexposure to MRI scanner 16 may be in addition to or instead of selectingdifferent MRI operating modes. For example, IMD 32 may select one of aplurality of exposure operating modes based on the type of MRI scannerand adjust one or more settings for use in the normal operating modeafter exposure to MRI scanner 16 based on the type of MRI scanner. Inanother example, IMD 32 may select the same exposure operating mode forany type of MRI scanner (e.g., without regard to the type of MRI scanner16), but adjust one or more settings for use in the normal operatingmode after exposure to MRI scanner 16 based on the type of MRI scanner.

IMD 32 may adjust the pacing amplitude and/or pacing pulse width for usewhen IMD 32 returns to the normal operating mode after exposure to MRIscanner 16, and the amount of adjustment may be determined based on thetype of MRI scanner. For example, IMD 32 may adjust the pacing amplitudeand/or pulse width by a first amount when exposed to a 1.5 T MRI scannerand adjust the pacing amplitude and/or pulse width by a second amountwhen exposed to a 3.0 T MRI scanner. The first amount may be larger thanthe second amount or smaller than the second amount. In another aspect,the first or second amount may be equal to zero. In this manner, thepacing amplitude and/or pulse width may be unchanged when exposed to onetype of MRI scanner and adjusted when exposed to another type of MRIscanner. In one instance, the adjustment may be an increase in pacingamplitude and/or pulse width. Such an adjustment may account for changesin pacing thresholds caused by exposure to MRI scanner 16, therebyincreasing the efficacy of the therapy.

Other settings used during the normal operating mode may be adjustedbased on the type of MRI scanner 16 in addition to or instead of thepacing amplitude or pulse widths. IMD 32 may adjust sensitivity of asense amplifier of IMD 32 after exposure to MRI scanner 16 and theamount of adjustment may be dependent on the type of MRI scanner in asimilar manner as described above with respect to pacing amplitudeand/or pulse width. For example, IMD 32 may increase the sensitivity ofthe sense amplifier by a first amount when exposed to a 1.5 T MRIscanner and increase the sensitivity of the sense amplifier by a secondamount when exposed to a 3.0 T MRI scanner. As another example, IMD 32may decrease the sensitivity of the sense amplifier by a first amountwhen exposed to a 1.5 T MRI scanner and decrease the sensitivity of thesense amplifier by a second amount when exposed to a 3.0 T MRI scanner.The first amount may be larger than the second amount or smaller thanthe second amount. In another aspect, the first amount or second amountmay be equal to zero. In a further example, IMD 32 may decrease thesensitivity of the sense amplifier when exposed to a first type of MRIscanner and increase the sensitivity of the sense amplifier by a secondamount when exposed to a second type of MRI scanner. Such adjustmentsmay account for changes in sensing thresholds caused by exposure to MRIscanner 16.

Prior to enabling the exposure operating mode, processor 60 operates IMD32 in accordance with settings programmed by a physician,electrophysiologist, clinician or other user, referred to herein as thenormal operating mode. The normal operating mode may correspond with theoperating mode that a physician or other user feels provides a mostefficacious therapy for patient 12. The normal operating mode may varyfrom patient to patient depending on the condition of patient 12 forwhich IMD 32 is providing therapy. In some instances, the normaloperating mode may be adaptive in that the normal operating modeactually includes switching between more than one pacing mode based onthe condition of the patient, such as described in U.S. Pat. No.7,130,683 to Casavant et al., entitled, “PREFERRED ADI/R: A PERMANENTPACING MODE TO ELIMINATE VENTRICULAR PACING WHILE MAINTAINING BACKUPSUPPORT,” which issued on Oct. 31, 2006 and which is incorporated hereinby reference in its entirety.

The normal operating mode of IMD 32 may be one or more of any of anumber of pacing modes, including DDD, VVI, DVI, VDD, AAI, DDI, DDDR,VVIR, DVIR, VDDR, AAIR, DDIR, VOO, AOO, DOO, ODO and other modes ofsingle and dual-chamber pacing or sensing. For example, the normaloperating mode may be an atrial based pacing mode, such as AAI or ADIpacing mode, if IMD 32 is providing therapy to a patient experiencingbradycardia. As another example, the normal operating mode may be adual-chamber pacing mode, such as a DDD pacing mode, if IMD 32 isproviding therapy to a patient with unreliable A-V conduction.

In the aforementioned operating modes, the abbreviations of whichconform to the NBG Pacemaker Code, the first letter in the pacing modeindicates the chamber or chambers paced and may take on the letter “D”indicating dual-chamber (i.e., atrial and ventricle both paced), “V”indicating a ventricle is paced, “A” indicating an atrium is paced, or“O” indicating no chamber is paced. The second letter indicates thechamber or chambers sensed and may take on the letter “D” indicatingdual-chamber (i.e., atrial and ventricle both paced), “V” indicating aventricle is paced, “A” indicating an atrium is paced, or “O” indicatingno chamber is paced. The third letter indicates mode or modes ofresponse to sensing and may take on the letter “T” indicating triggeredpacing (i.e., pacing is provided in response to the sensing), “I”indicating inhibited pacing (i.e., pacing is stopped based in responseto the sensing), “D” indicating dual response (i.e., triggered andinhibited) and “O” for no response. The fourth letter indicatesprogrammable functions and may take on the letter “R” indicating ratemodulated pacing, as well as other letters not explained here. Althoughnot described here, a fifth letter may be provided in accordance withthe NBG Pacemaker Code indicating anti-tachycardia functions.

When IMD 32 is configured to generate and deliver therapy to heart 38,control processor 60 controls stimulation module 66 to deliverelectrical stimulation therapy to heart 38 via one or more of electrodes44, 46, 50, 52 and/or the housing electrode. Stimulation module 66 iselectrically coupled to electrodes 44, 46, 50 and 52, e.g., viaconductors of the respective lead 34 and 36, or, in the case of thehousing electrode, via an electrical conductor disposed within thehousing of IMD 32. Control processor 60 controls stimulation module 66to generate and deliver electrical pacing pulses with the amplitudes,pulse widths, rates, electrode combinations or electrode polaritiesspecified by a selected therapy program. For example, electricalstimulation module 66 may deliver bipolar pacing pulses via ringelectrodes 46 and 52 and respective corresponding helical tip electrodes44 and 50 of leads 34 and 36, respectively. Stimulation module 66 maydeliver one or more of these types of stimulation in the form of othersignals besides pulses or shocks, such as sine waves, square waves, orother substantially continuous signals. In addition to pacing pulses,stimulation module 66 may, in some instances, deliver other types ofelectrical therapy, such as defibrillation, cardioversion and/or cardiacresynchronization therapy.

Processor 60 may include a pacer timing and control module (not shown),which may be embodied as hardware, firmware, software, or anycombination thereof. The pacer timing and control module may comprise adedicated hardware circuit, such as an ASIC, separate from othercomponents of control processor 60, or comprise a software moduleexecuted by a component of control processor 60, which may be amicroprocessor or ASIC. In other instances, the pacer timing and controlmodule may be part of stimulation module 66.

The pacer timing and control module may include programmable counterswhich control the basic time intervals associated with various singleand dual-chamber pacing modes. Intervals defined by the pacer timing andcontrol module within control processor 60 may include, for example,atrial and ventricular pacing escape intervals and refractory periodsduring which sensed atrial and ventricular events are ineffective torestart timing of the escape intervals. As another example, the pacetiming and control module may define a blanking period, and providesignals to sensing module 62 to blank one or more channels, e.g.,amplifiers, for a period during and after delivery of electricalstimulation to heart 38. The durations of these intervals may bedetermined by control processor 60 in response to parameters of theoperating mode, which are stored in memory 72. The pacer timing andcontrol module of control processor 60 may also determine the amplitudeand pulse width of the cardiac pacing pulses.

During pacing, escape interval counters within the pacer timing andcontrol module of control processor 60 may be reset upon sensing ofR-waves and P-waves with detection channels of sensing module 62.Additionally, the value of the count present in the escape intervalcounters when reset by sensed R-waves and P-waves may be used by controlprocessor 60 to measure the durations of R-R intervals, P-P intervals,P-R intervals and R-P intervals, which are measurements that may bestored in memory 72. Control processor 60 may analyze these variousintervals to determine conditions of heart 38, such as to detect atachyarrhythmia event. When IMD 32 is capable of providingdefibrillation therapy, the R-R intervals may be used to increment a VFcounter to control delivery of cardioversion or defibrillation shocks.For example, the VF counter may be incremented in response to detectionof short R-R intervals, and possibly in response to other events such asR-R interval variance. The VF counter triggers delivery of adefibrillation shock when the counter reaches a number of intervals fordetection (NID) threshold. Additionally, control processor 60 may beginan anti-tachyarrhythmia pacing regimen prior to delivery of thedefibrillation shock.

Sensing module 62 is configured to receive signals from one or moresensors. In one example, sensing module 62 is configured to receivesignals sensed by one or more of electrodes 44, 46, 50, 52 and thehousing electrode. In this manner, electrodes 44, 46, 50, 52, and thehousing electrode may operate as sense electrodes in addition to orinstead of being used for delivering electrical stimulation therapy. Inother instances, leads 34 and 36 may include one or more electrodesdedicated for sensing. In further examples, sensing module 62 is coupledto one or more sensors that are not included on leads 34 and 36, e.g.,via a wired or wireless coupling. Such sensors may include, but are notlimited to, pressure sensors, accelerometers, flow sensors, bloodchemistry sensors, activity sensors or other type of physiologicalsensor. Signals monitored by sensing module 62 may be stored in memory72.

Sensing module 62 may include one or more detection channels, each ofwhich may comprise a sense amplifier. The detection channels may be usedto sense cardiac signals. Some detection channels may detect events,such as R- or P-waves, and provide indications of the occurrences ofsuch events to processor 60. One or more other detection channels mayprovide the signals to an analog-to-digital converter, for processing oranalysis by processor 60. In response to the signals from processor 60,a switch module (not shown) within sensing module 62 may couple selectedelectrodes to selected detection channels.

For example, sensing module 62 may comprise one or more narrow bandchannels, each of which may include a narrow band filteredsense-amplifier that compares the detected signal to a threshold. If thefiltered and amplified signal is greater than the threshold, the narrowband channel indicates that a certain electrical cardiac event, e.g.,depolarization, has occurred. Processor 60 then uses that detection inmeasuring frequencies of the sensed events. Different narrow bandchannels of sensing module 62 may have distinct functions. For example,some various narrow band channels may be used to sense either atrial orventricular events.

In one example, at least one narrow band channel may include an R-waveamplifier that receives signals from the sensing configuration ofelectrodes 44 and 46, which are used for sensing and/or pacing in rightventricle 42 of heart 38. In addition, in some examples, a narrow bandchannel may include a P-wave amplifier that receives signals fromelectrodes 50 and 52, which are used for pacing and sensing in rightatrium 40 of heart 38. The R-wave and P-wave amplifier may take the formof an automatic gain controlled amplifier that provides an adjustablesensing threshold. Other amplifiers may also be used. Furthermore, insome examples, one or more of the sensing channels of sensing module 62may be selectively coupled to the housing electrode, with or instead ofone or more of electrodes 44, 46, 50 or 52, e.g., for unipolar sensingof R-waves or P-waves.

In some examples, sensing module 62 includes a wide band channel whichmay comprise an amplifier with a relatively wider pass band than theR-wave or P-wave amplifiers. Signals from the sensing electrodes thatare selected for coupling to this wide-band amplifier may be convertedto multi-bit digital signals by an analog-to-digital converter providedby, for example, sensing module 62 or processor 60. In some examples,processor 60 may store the digitized versions of signals from the wideband channel as electrograms (EGMs) in memory 72. Processor 60 mayemploy digital signal analysis techniques to characterize the digitizedsignals from the wide band channel to, for example detect and classifythe patient's heart rhythm. Processor 60 may detect and classify thepatient's heart rhythm by employing any signal processing methodologiesappropriate for the intended application or applications of IMD 32.Processor 60 may then control stimulation module 66 based on the signalssensed by sensing module 62.

As described above, the normal operating mode of IMD 32 may besusceptible to undesirable operation when IMD 32 is placed withinenvironment 10 with disruptive energy field 11. In some instances,sensing module 62 inappropriately detects the induced energy on theleads as physiological signals (e.g., intrinsic cardiac events). Inother words, IMD 32 senses a physiological signal when one is notactually present. At the very least, the detection of the induced energycaused by disruptive energy field 11 results in the stored data notaccurately representing the actual function and condition of heart 38.Moreover, the detection of the induced energy caused by disruptiveenergy field 11 may in turn cause undesirable operation of IMD 32.

For example, when the current or normal operating mode is a pacing modewith inhibit response to sensing, processor 60 may not deliver (i.e.,withhold) a desired pacing pulse in response to sensing the inducedenergy from disruptive energy field 11 as a physiological signal. Forexample, processor 60 may identify the induced energy as a ventricularevent. This may result in control processor 60 resetting the ventricularescape interval counter, thereby inhibiting delivery of a desired pacingpulse. In other instances when the normal operating mode is a dualchamber pacing mode with inhibit and trigger response to sensing,processor 60 may also deliver an undesirable pacing pulse in addition towithholding a desired pacing pulse in response to sensing the inducedenergy from disruptive energy field 11 as a physiological signal. Inparticular, sensing the induced energy from the disruptive energy fieldas a physiological signal may inappropriately start an escape intervalafter which an undesired pacing pulse is delivered. This may result indangerously fast heart rhythms and may lead to tachyarrhythmia orfibrillation.

In other instances, the induced energy on the leads may result in IMD 32not sensing actual physiological signals that are present. Processor 60may, for example, initiate a blanking period in response to the inducedenergy on the leads. During the blanking period, sensing module 62 maypower down one or more sense amplifiers. As such, sensing module 62 willfail to detect any intrinsic physiological event that occurs during theblanking period. Failure to detect this actual physiological event mayagain result in IMD 32 delivering undesired therapy or withholdingdesired therapy.

In further instances, the induced energy on one or more of leads 34 and36 or on one or more components of IMD 32 may result in inadvertentstimulation or heating of the tissue and/or nerve site adjacent to anyof electrodes 44, 46, 50 and 52 of respective leads 34 and 36 or thehousing of IMD 32. Such heating may compromise pacing and sensingthresholds at the tissue site, which could result in reduced therapyefficacy.

To reduce the adverse effects of disruptive energy field 11, controlprocessor 60 may be configured to operate IMD 32 in the exposureoperating mode as described in detail above. The exposure operating modeis typically less susceptible to undesirable operation in disruptiveenergy field 11 than the normal operating mode. In other words,operating IMD 32 in the exposure mode may reduce, if not eliminate, someor all of the adverse effects that disruptive energy field 11 have ontherapy delivery to patient 12. When operating in the exposure operatingmode, control processor 60 is configured to operate with differentfunctionality compared to the normal operating mode. Processor 60 may,in some instances, be configured to operate with reduced functionality.For example, processor 60 may not provide sensing, not deliver therapy,delivery only a subset of possible therapies, not log collected data orthe like. In other instances, processor 60 may be operating withapproximately the same functionality or even increased functionality inthe exposure mode. For example, processor 60 may use a different sensoror algorithm to detect cardiac activity of the heart of patient 12, suchas pressure sensor measurements rather than electrical activity of theheart.

Processor 60 may receive the parameters of the exposure operating modefrom a user via programming device 18. In other words, the exposureoperating mode parameters may be manually configured by the user. Inanother example, at least a portion, and in some cases all, of theparameters of the exposure operating mode may be automaticallydetermined One example technique for automatically determining one ormore parameters of the exposure operating mode is described inco-pending patent application Ser. No. 12/569,101 to Ellingson et al.,entitled, “AUTOMATIC SELECTION OF PARAMETERS OF AN EXPOSURE MODE OF ANIMPLANTABLE MEDICAL DEVICE,” which was filed on Sept. 29, 2009 and whichis incorporated herein by reference in its entirety. Whether theparameters were manually entered or automatically determined or both,processor 60 may store the parameters of the exposure operating mode inmemory 72.

Control processor 60 may include any one or more of a microprocessor, acontroller, a DSP, ASIC, FPGA, or equivalent discrete or integratedcircuitry, including analog circuitry, digital circuitry, or logiccircuitry. The functions attributed to control processor 60 herein maybe embodied as software, firmware, hardware or any combination thereof.

Memory 72 may include computer-readable instructions that, when executedby control processor 60 or other component of IMD 32, cause one or morecomponents of IMD 32 to perform various functions attributed to thosecomponents in this disclosure. Memory 72 may include any volatile,non-volatile, magnetic, optical, or electrical media, such as a randomaccess memory (RAM), read-only memory (ROM), non-volatile RAM (NVRAM),static non-volatile RAM (SRAM), electrically-erasable programmable ROM(EEPROM), flash memory, or any other computer-readable storage media.

The various components of IMD 32 are coupled to power source 74, whichmay include a rechargeable or non-rechargeable battery. Anon-rechargeable battery may be capable of holding a charge for severalyears, while a rechargeable battery may be inductively charged from anexternal device, e.g., on a daily or weekly basis. Power source 74 alsomay include power supply circuitry for providing regulated voltagesand/or current levels to power the various components of IMD 32.

Under the control of processor 60, telemetry module 70 may receivedownlink telemetry from and send uplink telemetry to programming device18 with the aid of an antenna 78, which may be internal and/or externalto IMD 32. Telemetry module 70 includes any suitable hardware, firmware,software or any combination thereof for communicating with anotherdevice, such as programming device 18. For example, telemetry module 70may include appropriate modulation, demodulation, encoding, decoding,frequency conversion, filtering, and amplifier components fortransmission and reception of data.

The various modules of IMD 32 may include one or more processors, suchas one or more microprocessors, DSPs, ASICs, FPGAs, programmable logiccircuitry, or the like, that may perform various functions andoperations, such as those described herein.

FIG. 4 is a functional block diagram illustrating control processor 60,disruptive field detector 68 and memory 72 in further detail. Processor60 of FIG. 4 includes an MRI detection module 80 having a presencedetection module 81 and a type determination module 82 and a parameteradjustment module 83 having an exposure mode selection module 84 and anormal mode adjustment module 85. Disruptive field detector 68 of FIG. 4includes an RF sensor 86 and a magnetic field sensor 88. Controlprocessor 60, memory 72 and/or disruptive field detector 68 may includemore or fewer components based on particular implementation of thetechniques of this disclosure.

MRI presence detection module 81 of processor 60 detects a conditionindicative of the presence of MRI scanner 16. MRI presence detectionmodule 81 inputs signals from one or more of disruptive field detector68, antenna 78, lead 34 or lead 36. MRI presence detection module 81detects a condition indicative of the presence of MRI scanner 16 basedon the signals. In one example, MRI presence detection module 81 maydetect the condition indicative of the presence of MRI scanner 16 basedon input from magnetic field sensor 88, which may vary as a function ofthe magnitude of the magnetic field. MRI presence detection module 81may detect the condition indicative of the presence of MRI scanner 16when the signal from magnetic field sensor 88 exceeds a threshold.Magnetic field sensor 88 may, for example, comprise a Hall effectsensor, magnetoresistive sensor or other magnetic field sensor. MRIpresence detection module 81 may, however, detect the presence of MRIscanner 16 using other signals detected by any one of or a combinationof disruptive field detector 68, antenna 78, lead 34 or lead 36.

MRI type determination module 82 determines a type of MRI scanner inresponse to detecting the presence of MRI scanner 16. MRI typedetermination module 82 inputs signals from one or more of disruptivefield detector 68, antenna 78, lead 34 or lead 36 and analyzes thesignals to determine the type of MRI scanner. In one example, MRI typedetermination module 82 may determine the type of MRI scanner based onthe same signals used by MRI presence detection module 81 for detectingthe presence of MRI scanner 16. MRI type determination module 82 maydetermine that MRI scanner 16 is a 1.5 T MRI scanner if the output ofmagnetic field sensor 88 is in a first range and determine MRI scanner16 is a 3.0 T MRI scanner when the output of magnetic field sensor 88 isin a second range. As such, MRI type determination module 82 maydetermine the type of MRI scanner based on the same signals used todetect the condition indicative of the presence of MRI scanner 16. Insome instances, MRI presence detection module 81 and MRI typedetermination module 82 may be viewed as concurrently detecting thepresence and type of MRI scanner 16, respectively. In such a case, MRIpresence detection module 81 and MRI type determination module 82 may bea single module.

In another example, MRI type determination module 82 determines the typeof MRI scanner based on signals from one or more other sources inaddition to or instead of the signals received from magnetic fieldsensor 88. For instance, upon detecting the condition indicative of thepresence of MRI scanner 16 (e.g., magnitude of magnetic field exceeds athreshold), MRI type determination module 82 may determine a frequencyof RF energy emitted subsequent to detecting the presence of MRI scanner16 to determine the type of scanner. MRI type determination module 82may determine that the MRI scanner is a 1.5 T scanner when the frequencyof RF energy is approximately 64 MHz and determine that the MRI scanneris a 3.0 T MRI scanner when the frequency of the RF energy isapproximately 128 MHz.

To this end, MRI type determination module 82 receives input from one ormore components that receive the RF energy emitted by MRI scanner 16.For example, MRI type determination module 82 may receive input from RFsensor 86 of disruptive field detector 68. RF sensor 86 may include oneor more coils, stubs, or other structure that operates as an antenna toreceive RF energy. The structures or “antennas” of RF sensor 86 may betuned to a frequency that is approximately equal to the frequency of theRF energy of the MRI scanner (e.g., 64 or 128 MHz in the case of a 1.5 Tor 3.0 T MRI scanner). RF sensor 86 may also include a frequencydetector that may, for example, determine when the energy induced on theantennas of RF sensor 86 exceeds a threshold. RF sensor 86 may send asignal to processor 86 indicating that RF energy of a particularfrequency has been detected. Alternatively, the frequency detectioncircuitry may be implemented within MRI type determination module 82 andRF sensor 86 simply passes the induced energy to MRI type determinationmodule 82 for determination as to whether RF energy of a particularfrequency is detected.

As another example, MRI type determination module 82 may receive asignal from antenna 78 and use that signal to determine whether RFenergy of a particular frequency (e.g., RF energy of a frequencycorresponding to a particular type of MRI scanner) is received. Althoughantenna 78 may not be tuned to the frequency utilized by MRI scanner 16,the pulsed RF signals of MRI scanner 16 may induce a signal on antenna78. MRI type determination module 82 may determine the frequency of theRF energy using the signal induce on antenna 78 to identify the type ofMRI scanner.

In another example, MRI type determination module 82 may receive asignal from one of leads 34 or 36 and use that signal to determinewhether RF energy of a particular frequency (e.g., RF energy of afrequency corresponding to a particular type of MRI scanner) isreceived. Conductors within leads 34 and 36 may act as an antenna whenplaced in environment 10. In other words, the pulsed RF signals of MRIscanner 16 may induce a signal on one of more of the conductors withinleads 34 or 36. MRI type determination module 82 may analyze the inducedsignals on conductors of leads 34 or 36 to determine the frequency ofthe RF energy and identify the type of MRI scanner. MRI typedetermination module 82 may, in some instances, determine the frequencyof the RF energy using multiple sources, i.e., a combination of RFsensor 86, antenna 78, lead 34 or lead 36, or other mechanism fordetermining the frequency of RF energy. MRI type determination module 82may also use the various sources as an antenna diversity scheme for usein detecting the type of MRI device.

In the examples described above, MRI presence detection module 81 maydetect the presence of MRI scanner 16 based on the existence of a strongmagnetic field and MRI type determination module 82 may determine thetype of MRI scanner based on the frequency of RF energy. MRI presencedetection module 81 may, however, detect the presence of MRI scanner 16using other signals detected by any one or a combination of disruptivefield detector 68, antenna 78, lead 34 or lead 36. Likewise, MRI typedetermination module 82 may determine the type of MRI scanner usingother signals detected by any one of or a combination of disruptivefield detector 68, antenna 78, lead 34 or lead 36.

Based on the determination of the type of MRI scanner, exposure modeselection module 84 may select an appropriate exposure operating mode,e.g., by retrieving exposure mode operating parameters corresponding tothe type of MRI scanner, and configure IMD 32 to operate in accordancewith the retrieved operating parameters. For example, exposure modeselection module 84 may retrieve first exposure mode operatingparameters 90 from memory 72 in response to determining that the MRIscanner is a 1.5 T MRI scanner and select second exposure mode operatingparameters 92 from memory 72 in response to determining that the MRIscanner is a 3.0 T MRI scanner.

As described above, first exposure mode operating parameters 90 andsecond exposure mode operating parameters 92 include at least oneoperating parameter that is specifically tailored for exposure to aparticular type of MRI scanner. For example, processor 60 may implementa filter to attenuate signals at a first frequency (e.g., 64 MHz) whenoperating in the exposure operating mode corresponding to a 1.5 T MRIscanner and implement a filter to attenuate signals at a secondfrequency (e.g., 128 MHz) when operating in the exposure operating modecorresponding to a 3.0 T MRI scanner. Additionally or alternatively,processor 60 may control stimulation module 66 to deliver therapy havinga different pacing amplitude and/or pulse width based on the type of MRIscanner as described in detail above.

However, exposure mode operating parameters 90 and 92 may include somecommon operating parameters. In other words, some parameters ofoperating parameters 90 and 92 may be the same regardless of the type ofMRI scanner. For example, exposure mode operating parameters 90 and 92may include the same pacing mode, pacing amplitude, pacing pulse width,pacing rate, or other operating parameter. As such, although each of theexposure operating modes may include operating parameters specificallytailored for operation in a particular MRI environment, exposure modeoperating parameters 90 and 92 may include at least some operatingparameters in common.

Because of the commonality in some (or many) of the operating parametersof the different exposure operating modes, processor 60 may configureIMD 32 to operate in accordance with the common operating parametersprior to determining the type of MRI scanner. For example, processor 60may retrieve common exposure mode operating parameters 94 from memory 72upon detecting the presence of an MRI scanner (e.g., upon detecting alarge static magnetic field) and then retrieve the operating parameters90 or 92 that are specific to the type of MRI scanner upon detecting thetype of MRI scanner (e.g., based on the frequency of the RF energy). Inthis manner, processor 60 may reduce the effect of any MRI scannerimmediately upon exposure to the MRI scanner and further reduce theeffect of the particular type of MRI scanner upon determining the typeof MRI scanner.

In other aspects, normal mode adjustment module 85 may adjust one ormore parameters to use when IMD 32 returns to the normal operating modeafter exposure to MRI scanner 16. Normal mode adjustment module 85 may,for example, determine the parameter or parameter(s) to adjust and theamount of adjustment necessary based on the type of MRI scanner. Thenormal operating mode parameters 96 may be stored in memory 72 andnormal mode adjustment module 85 may read and write new values to normaloperation mode parameters 96 of memory 72 based on the type of MRIscanner. Normal mode adjustment module 85 may, for example, adjust oneor more of a pacing amplitude, pacing pulse width, a sensitivity of asense amplifier or other parameter that is used during the normaloperating mode.

The adjustment of the one or more parameters for use in the normaloperating mode after exposure to MRI scanner 16 may be in addition to orinstead of selecting different MRI operating modes. For example, IMD 32may select one of a plurality of exposure operating modes based on thetype of MRI scanner and adjust one or more settings for use in thenormal operating mode after exposure to MRI scanner 16 based on the typeof MRI scanner. In another example, IMD 32 may select the same exposureoperating mode for any type of MRI scanner (e.g., without regard to thetype of MRI scanner 16), but adjust one or more settings for use in thenormal operating mode after exposure to MRI scanner 16 based on the typeof MRI scanner.

FIG. 5 is a functional block diagram illustrating example components ofIMD 32 for implementing exposure operating modes tailored for specifictypes of MRI scanners. As described in detail above, processor 60determines the type of MRI scanner based on one or more detectedconditions. In response to determining the type of MRI scanner,processor 60 may retrieve operating mode parameters corresponding to thetype of MRI scanner and configure IMD 32 to operate in accordance withthe retrieved operating parameters.

IMD 32 may, in one example, include filters 96A-96D and filters 98A-98D(collectively “filters 96” and “filters 98,” respectively). In theexample illustrated in FIG. 5, filters 96 and 98 are coupled betweenrespective electrodes of leads 34 and 36 and sensing module 62 andstimulation module 66. For example, filter 96A and 98A are connectedbetween electrode 44 of lead 34 and modules 62 and 66. Likewise, filters96B and 98B are connected between electrode 46 of lead 34 and modules 62and 66, filters 96C and 98C are connected between electrode 50 of lead36 and modules 62 and 66, and filter 96D and 98D are connected betweenelectrode 52 of lead 36 and modules 62 and 66. Each of filters 96 isconfigured to suppress signals with frequencies approximately equal to64 MHz and each of filters 98 is configured to suppress signals withfrequencies approximately equal to 128 MHz. In one example, filters 96and 98 may be band-stop filters, such as notch filters, designed tosuppress signals around the desired frequencies, e.g., 64 MHz and 128MHz, respectively.

Upon determining the type of MRI scanner, processor 60 selects theappropriate ones of filters 96 and 98 based on the type of MRI scannerand applies the selected filter to signals on conductors of leads 34 and36. For a 1.5 T scanner, which generates pulsed RF energy at 64 MHz,processor 60 may apply filters 96A-96D to the signals on the respectiveconductors to which filters 96 are connected. For a 3.0 T scanner, whichgenerates pulsed RF energy at 128 MHz, processor 60 may apply filters98A-98D to the signals on the respective conductors to which filters 98are connected. In this manner, the exposure operating mode is tailoredfor the type of MRI scanner that is detected.

Filters 96 and 98 may, in one example, be absorptive filters that absorbthe unwanted RF energy. In this case, filters 96 and 98 absorb the RFenergy into the device instead of reflecting the RF energy back towardthe electrodes on leads 34 and 36. Absorbing the RF energy at the devicemay reduce the amount of heating that occurs adjacent to electrodes 44,46, 50 and 52 of leads 34 and 36. In another example, filters 96 and 98may be reflective filters that reflect the unwanted RF energy away fromthe device. In either case, the RF energy induced on leads 34 and 36 isattenuated, thus increasing the accuracy with which sensing module 62may sense cardiac signals of heart 38. Prior to operating IMD 32 in oneof the exposure operating modes, signals on conductors of leads 34 and36 may go unfiltered into sensing module 62 or filtered using filterfeed through capacitors in the connector block 54.

Filters 96 and 98 may include one or more capacitive elements, inductiveelements and resistive elements. In some instances, each of filters 96and 98 may be separate components, e.g., include separate capacitive,inductive and resistive elements. Processor 60 may switch between thefilters based on the type of MRI scanner. In other instances, filters 96may share one or more capacitive, inductive or resistive elements withcorresponding filter 98. For example, filter 96A and 98 may share one ormore capacitive, inductive or resistive elements. In this case,processor may switch in one or more additional elements or adjust theshared elements to tune the filters to the appropriate frequency basedon the type of MRI. The capacitive, inductive and resistive elements maybe discrete components or may be intrinsic characteristics of componentsthat also serve an additional purpose, such as channel capacitors, laserribbon bonds, feed through capacitors, or some intrinsic property ofanother component of IMD 32.

Filters 96 and 98 may be located within a housing of IMD 32, within aconnector block of IMD 32, or partially located within the housing andthe connector block. In other instances, filters 96 and 98 may belocated within the body of leads 34 and 36, e.g., at a proximal end nearIMD 32 or at a distal end near electrodes of leads 34 and 36.

FIG. 6 is a flow diagram illustrating an example operation of an IMD,such as IMD 32 or IMD 14, selecting an exposure operating mode based onthe type of MRI scanner. In FIG. 6, processor 60 of IMD 32 detects acondition indicative of a presence of MRI scanner 16 (100). Presencedetection module 82 of processor 60 may receive a signal from one ormore sources, including disruptive field detector 68, antenna 78, lead34 or lead 36 and analyze the signal to detect the condition indicativeof the presence of MRI scanner 16. In one example, presence detectionmodule 81 may detect the presence of MRI scanner 16 upon detecting amagnetic field having a magnitude that is larger than a threshold.

Processor 60 determines the type of MRI scanner (102). Typedetermination module 82 of processor 60 may determine the type of MRIscanner based on the signals used to detect the presence of MRI scanner16, based on one or more other signals or based on the signals used todetect the presence of MRI scanner 16 and one or more other conditions.For example, type determination module 82 may determine that MRI scanner16 is a 1.5 T MRI scanner when the magnetic field has a magnitude withina first threshold range corresponding to the 1.5 T MRI scanner anddetermine that MRI scanner 16 is a 3.0 T MRI scanner when the magneticfield has a magnitude within a first threshold range corresponding tothe 3.0 T MRI scanner. As another example, type determination module 82may determine the type of MRI scanner based a frequency of RF energygenerated by MRI scanner 16. Type determination module 82 may determinethat the MRI scanner is a 1.5 T scanner when the frequency of RF energyis approximately 64 MHz and determine that the MRI scanner is a 3.0 TMRI scanner when the frequency of the RF energy is approximately 128MHz.

Processor 60 selects an exposure operating mode corresponding to thetype of MRI scanner (104). For example, exposure mode selection module84 of processor 60 may select operating parameters of a first exposureoperating mode for a 1.5 T MRI scanner and select operating parametersof a second exposure operating mode for a 3.0 T MRI scanner. Theselected exposure operating mode may include at least one operatingparameter that is specifically tailored for exposure to a particulartype of MRI scanner. For example, processor 60 may implement a filter toattenuate signals at a first frequency (e.g., 64 MHz) when operating inthe exposure operating mode corresponding to a 1.5 T MRI scanner andimplement a filter to attenuate signals at a second frequency (e.g., 128MHz) when operating in the exposure operating mode corresponding to a3.0 T MRI scanner. However, some of the operating parameters may be thesame for each of the exposure operating modes, such as the pacing mode,pacing pulse amplitude, pacing pulse width, pacing rate, or the like.Processor 60 configures IMD 32 to operate in the selected exposureoperating mode corresponding to the type of MRI scanner (106).

Processor 60 may adjust one or more parameters of the normal operatingmode based on the determination of the type of MRI scanner (108). Inother words, processor 60 may adjust one or more parameters for use whenIMD 32 returns to the normal operating mode after exposure to MRIscanner 16. For example, normal mode adjustment module 85 may adjust theone or more parameter of the normal operating mode by a first amountwhen exposed to a first type of MRI scanner (e.g., a 1.5 T MRI scanner)and adjust the parameter by a second amount when exposed to a secondtype of MRI scanner (e.g., a 3.0 T MRI scanner). The first amount may belarger than the second amount or smaller than the second amount. Inanother aspect, the first or second amount may be equal to zero suchthat the parameter is unchanged when exposed to one type of MRI scannerand adjusted when exposed to another type of MRI scanner. The one ormore parameters of the normal operating mode may include, for example, apacing amplitude, a pacing pulse width, a sensitivity of a senseamplifier or other parameter that may need to be changed due to theexposure of IMD 32 to MRI scanner 16. Processor 60 may, in someinstances, not adjust any parameters of the normal operating mode basedon the determination of the type of MRI scanner.

Processor 60 configures IMD 32 from the exposure operating mode to thenormal operating mode after completion of the MRI scan (109). In oneexample, processor 60 may automatically configure IMD 32 from theexposure operating mode to the normal operating mode, e.g., in responseto disruptive field detector 68 no longer detecting disruptive energyfield 11 of MRI scanner 16, after a predetermined period of time (e.g.,one hour), or other condition, or a combination of two or moreconditions. In another example, processor 60 may configure IMD 32 fromthe exposure operating mode to the normal operating mode manually viainteraction with programming device 18.

FIG. 7 is a flow diagram illustrating an example operation of an IMD,such as IMD 32 or IMD 14, detecting the presence of an MRI scanner anddetermining the type of MRI scanner. Processor 60 of IMD 32 determines amagnitude of a static magnetic field to which IMD 32 is exposed (110).Processor 60 may, for example, obtain a signal from magnetic fieldsensor 88, which may vary as a function of the magnitude of the magneticfield, and analyze the signal to determine the magnitude of the magneticfield.

Processor 60 determines whether the magnitude of the static magneticfield is within a first range (111). The first range may correspond witha magnitude range of a magnet mode of operation. When processor 60determines that the magnitude of the static magnetic field is within thefirst range, processor 60 configures IMD 32 to operate in accordancewith the magnet mode (112). The magnetic mode of operation maycorrespond with an asynchronous pacing mode (e.g., DOO or VOO) and maybe used when a user wishes to establish communication with IMD 32, suchas during a follow-up visit.

When processor 60 determines that the magnitude of the static magneticfield is not within the first range, processor 60 determines whether themagnitude of the static magnetic field is within a second range (114).The second range may correspond with a magnitude range of a first typeof MRI scanner, e.g., a 1.5 T MRI scanner. When processor 60 determinesthat the magnitude of the static magnetic field is within the secondrange, MRI presence detection module 81 determines the presence of a 1.5T MRI scanner (116).

When processor 60 determines that the magnitude of the static magneticfield is not within the second range, processor 60 determines whetherthe magnitude of the static magnetic field is within a third range(118). The third range may correspond with a magnitude range of a secondtype of MRI scanner, e.g., a 3.0 T MRI scanner. When processor 60determines that the magnitude of the static magnetic field is within thethird range, MRI presence detection module 81 determines the presence ofa 3.0 T MRI scanner (122). In this manner, processor 60 may be viewed asconcurrently detecting the presence and type of MRI scanner based on themagnitude of the magnetic field. If the magnitude of the magnetic fielddoes not fall within any of the three ranges, processor 60 determinesthat no MRI scanner is present and maintains operating in accordancewith the current (or normal) operating mode (120).

In response to detecting the presence and type of MRI scanner, processor60 selects an exposure operating mode corresponding to the type of MRIscanner (124). For example, processor 60 may select operating parametersof a first exposure operating mode for a 1.5 T MRI scanner and selectoperating parameters of a second exposure operating mode for a 3.0 T MRIscanner. The selected exposure operating mode may include at least oneoperating parameter that is specifically tailored for exposure to aparticular type of MRI scanner. Processor 60 configures IMD 32 tooperate in the selected exposure operating mode corresponding to thetype of MRI scanner (126).

FIG. 8 is a flow diagram illustrating another example operation of anIMD, such as IMD 32 or IMD 14, detecting the presence of an MRI scannerand determining the type of MRI scanner. MRI presence detection module81 of processor 60 determines a magnitude of a static magnetic field towhich IMD 32 is exposed (130). MRI presence detection module 81 may, forexample, obtain a signal from magnetic field sensor 88, which may varyas a function of the magnitude of the magnetic field, and analyze thesignal to determine the magnitude of the magnetic field.

MRI presence detection module 81 determines whether the magnitude of thestatic magnetic field is greater than a threshold (132). The thresholdmay be a value that is larger than the magnetic field required to enterthe device into the magnet mode of operation and may encompass both themagnitude of the magnetic field generated by both 1.5 T and 3.0 T MRIscanners. When the magnitude of the magnetic field is not greater thanthe threshold, MRI presence detection module 81 continues to determinethe magnitude of the magnetic field to which IMD 32 is exposed. When themagnitude of the magnetic field is greater than the threshold, MRIpresence detection module 81 detects the presence of MRI scanner 16(134).

In some instances, processor 60 may configure IMD 32 to operate inaccordance with exposure mode operating parameters common to all MRIscanners upon detecting the presence of MRI scanner 16 (136). Forexample, processor 60 may retrieve common exposure mode operatingparameters 94 from memory 72 upon detecting the presence of an MRIscanner. In other instances, processor 60 may configure IMD 32 tooperate in a default exposure operating mode upon detecting the presenceof MRI scanner 16. In this manner, processor 60 may at least partiallyreduce the effect of any MRI scanner immediately upon exposure to theMRI scanner. Alternatively, processor 60 may not configure any exposuremode operating parameters until the type of MRI is detected.

MRI type determination module 82 of processor 60 determines a frequencyof RF energy emitted subsequent to detecting the presence of MRI scanner16 (138). To this end, MRI type determination module 82 receives signalsfrom one or more components that receive the RF energy emitted by MRIscanner 16, such as RF sensor 86, antenna 78, lead 34 or lead 36. MRItype determination module 82 determines whether the frequency of the RFenergy is approximately equal to 64 MHZ (140). When MRI typedetermination module 82 determines that the frequency is approximatelyequal to 64 MHz, MRI type determination module 82 determines thepresence of a 1.5 T MRI scanner, i.e., determines the type of MRIscanner (142).

When MRI type determination module 82 determines that the frequency isnot approximately equal to 64 MHz, MRI type determination module 82determines whether the frequency of the RF energy is approximately equalto 128 MHZ (144). When MRI type determination module 82 determines thatthe frequency is approximately equal to 128 MHz, MRI type determinationmodule 82 determines the presence of a 3.0 T MRI scanner, i.e.,determines the type of MRI scanner (146). When MRI type determinationmodule 82 determines that the frequency is not approximately equal to128 MHz, MRI type determination module 82 determines that the disruptiveenergy field is from a different source (e.g., a non-MRI source or adifferent type of MRI scanner) (147).

In response to detecting the type of MRI scanner, exposure modeselection module 84 of processor 60 selects an exposure operating modecorresponding to the type of MRI scanner (148). For example, processor60 may select operating parameters of a first exposure operating modefor a 1.5 T MRI scanner and select operating parameters of a secondexposure operating mode for a 3.0 T MRI scanner. The selected exposureoperating mode may include at least one operating parameter that isspecifically tailored for exposure to a particular type of MRI scanner.Processor 60 configures IMD 32 to operate in the selected exposureoperating mode corresponding to the type of MRI scanner (150).

FIG. 9 is a flow diagram illustrating an example operation of an IMD,such as IMD 32 or IMD 14, adjusting one or more parameters that will beused when IMD 32 returns to the normal operating mode based on the typeof MRI scanner. Processor 60 configures IMD 32 into an exposureoperating mode prior to or upon exposure to disruptive energy field 11(151). Processor 60 may automatically enable the exposure operatingmode, e.g., in response to detecting one or more conditions, or manuallyenable the exposure operating mode of IMD 32, e.g., via interaction withprogramming device 18.

IMD 32 detects a type of MRI scanner to which IMD 32 is exposed (152).IMD 32 may, for example, detect the type of MRI scanner using thetechniques described above with respect to FIG. 7 and FIG. 8. If IMD 32determines the detected type of MRI scanner is a first type, e.g., a 1.5T MRI scanner (“YES” branch of block 154), IMD 32 may adjust a parameterof the normal operating mode by a first amount (156). If IMD 32determines the detected type of MRI scanner to not be the first type ofMRI scanner (“NO” branch of block 154), IMD 32 determines whether thedetected type of MRI scanner is a second type of MRI scanner, e.g., a3.0 T MRI scanner (158). If IMD 32 determines the detected type of MRIscanner is the second type, e.g., a 3.0 T MRI scanner (“YES” branch ofblock 158), IMD 32 may adjust the parameter of the normal operating modeby a second amount (160). The second amount may be larger or smallerthan the first amount. In another aspect, the first or second amount maybe equal to zero such that the parameter is unchanged when exposed toone type of MRI scanner and adjusted when exposed to another type of MRIscanner.

The parameter of the normal operating mode may be, for example, a pacingamplitude, a pacing pulse width, a sensitivity of a sense amplifier orother parameter that may need to be changed due to the exposure of IMD32 to MRI scanner 16. IMD 32 may, in some instances, not adjust anyparameters of the normal operating mode based on the determination ofthe type of MRI scanner.

Processor 60 configures IMD 32 from the exposure operating mode to thenormal operating mode after completion of the MRI scan (162). Processor60 may automatically configure IMD 32 from the exposure operating modeto the normal operating mode or manually configure IMD 32 from theexposure operating mode to the normal operating mode via interactionwith programming device 18.

Although the techniques of this disclosure are described in the contextof detecting whether the MRI scanner is 1.5 T MRI scanner or a 3.0 T MRIscanner, the techniques may be applied to distinguish among other typesof MRI scanners. Moreover, the techniques may be further applied todistinguish between different types of other devices that generateinterfering signals, such as CT devices, electrocautery devices,diathermy devices, or the like.

The techniques described in this disclosure, including those attributedto IMD 14 and/or 32, may be implemented, at least in part, in hardware,software, firmware or any combination thereof. For example, variousaspects of the techniques may be implemented within one or moreprocessors, including one or more microprocessors, DSPs, ASICs, FPGAs,or any other equivalent integrated or discrete logic circuitry, as wellas any combinations of such components, embodied in programmers, such asphysician or patient programmers, stimulators, or other devices. Theterm “processor” may generally refer to any of the foregoing circuitry,alone or in combination with other circuitry, or any other equivalentcircuitry.

Such hardware, software, or firmware may be implemented within the samedevice or within separate devices to support the various operations andfunctions described in this disclosure. In addition, any of thedescribed units, modules or components may be implemented together orseparately as discrete but interoperable logic devices. Depiction ofdifferent features as modules or units is intended to highlightdifferent functional aspects and does not necessarily imply that suchmodules or units must be realized by separate hardware or softwarecomponents. Rather, functionality associated with one or more modules orunits may be performed by separate hardware or software components, orintegrated within common or separate hardware or software components.

When implemented in software, the functionality ascribed to the systems,devices and techniques described in this disclosure may be embodied asinstructions on a computer-readable medium such as RAM, ROM, NVRAM,SRAM, EEPROM, flash memory, magnetic data storage media, optical datastorage media, or the like. The instructions may be executed to supportone or more aspects of the functionality described in this disclosure.

Various examples have been described. These and other examples arewithin the scope of the following claims.

The invention claimed is:
 1. An implantable medical device comprising: amemory to store operating parameters for a plurality of exposureoperating modes, wherein the plurality of exposure operating modesincludes a default exposure operating mode and at least one operatingmode that corresponds to a particular type of magnetic resonance imaging(MRI) scanner; and a processor configured to detect a conditionindicative of a presence of an MRI scanner, configure the implantablemedical device to operate in accordance with operating parameters of thedefault exposure operating mode stored in the memory in response todetecting the presence of the MRI scanner, subsequently determine a typeof MRI scanner in response to detecting the condition, retrieve from thememory the operating parameters of the one of the plurality of exposureoperating modes corresponding to the determined type of MRI scanner, andconfigure the implantable medical device to operate in accordance withthe retrieved operating parameters.
 2. The device of claim 1, whereinthe processor includes an MRI detection module that detects thecondition indicative of the presence of the MRI scanner upon detectingat least one of a static magnetic field that exceeds a static fieldstrength threshold, a gradient magnetic field that exceeds a gradientfield strength threshold and a radio frequency (RF) signal of aparticular frequency.
 3. The device of claim 2, further comprising amagnetic field sensor that outputs a signal that varies as a function ofthe magnitude of a magnetic field, wherein the MRI detection moduleanalyzes the signal output by the magnetic field sensor to detect thecondition indicative of the presence of the MRI scanner.
 4. The deviceof claim 3, wherein the processor includes an MRI type determinationmodule that analyzes the output of the magnetic field sensor to detectthe type of the MRI scanner to which the implantable medical device isexposed.
 5. The device of claim 1 wherein the detected conditioncomprises a first condition, and the processor detects a secondcondition and determines the type of MRI scanner based on the seconddetected condition.
 6. The device of claim 5, wherein the processordetermines a frequency of RF energy to which the implantable medicaldevice is exposed and determines the type of MRI scanner based on thefrequency of the RF energy.
 7. The device of claim 6, further comprisingat least one of an RF sensor, an antenna and a conductor of a lead onwhich a signal is induced by RF energy emitted by the MRI scanner,wherein the processor analyzes the induced signal to determine afrequency of RF energy to which the implantable medical device isexposed.
 8. The device of claim 1, further comprising one or morefilters that are connected to respective conductors of one or more leadsextending from the implantable medical device, wherein the processorconfigures the one or more filters to attenuate a frequency associatedwith the determined type of MRI scanner.
 9. The device of claim 1,further comprising a magnetic field strength sensor and a radiofrequency (RF) sensor, wherein the processor is configured detect acondition indicative of the presence of the MRI scanner and configurethe implantable medical device to operate in accordance with operatingparameters of the default exposure operating in response to the magneticfield strength sensor detecting a magnetic field having a strength thatis greater than or equal to a threshold strength, and subsequentlydetermine the type of MRI scanner and configure the implantable medicaldevice to operate in accordance with the operating parameters of the oneof the plurality of exposure operating modes corresponding to thedetermined type of MRI scanner based on the output of the RF sensor. 10.A method comprising: detecting, with an implantable medical device, acondition indicative of a presence of a magnetic resonance imaging (MRI)scanner; configuring the implantable medical device to operate inaccordance with operating parameters of a default exposure operatingmode stored in the memory in response to detecting the presence of theMRI scanner; subsequently, determining, with the implantable medicaldevice, a type of the MRI scanner; selecting, with the implantablemedical device and based on the determination, a second exposureoperating mode that corresponds to operating parameters for use duringexposure to a particular type of MRI scanner; and configuring theimplantable medical device to operate in accordance with the operatingparameters of the selected exposure operating mode.
 11. The method ofclaim 10, wherein detecting the condition indicative of the presence ofthe MRI scanner comprises one of detecting a static magnetic field thatexceeds a static field strength threshold, detecting one or moregradient magnetic fields that exceed a gradient field strength thresholdand detecting one or more radio frequency (RF) signals of a particularfrequency.
 12. The method of claim 10, wherein determining the type ofMRI scanner comprises determining the type of MRI scanner based on thedetected condition.
 13. The method of claim 12, wherein detecting thecondition comprises detecting the condition based on a magnitude of amagnetic field to which the implantable medical device is exposed; anddetermining the type of MRI scanner comprises determining the type ofMRI scanner based on the magnitude of the magnetic field to which theimplantable medical device is exposed.
 14. The method of claim 10,wherein the detected condition comprises a first condition, the methodfurther comprising: detecting a second condition; and determining thetype of MRI scanner based on the second detected condition.
 15. Themethod of claim 14, wherein detecting the second condition comprises:determining a frequency of RF energy to which the implantable medicaldevice is exposed; and determining the type of MRI scanner based on thedetermined frequency of the RF energy.
 16. The method of claim 10,wherein configuring the implantable medical device to operate inaccordance with the operating parameters of the selected exposureoperating mode comprises configuring a filter to attenuate a frequencyassociated with the determined type of MRI scanner.
 17. The method ofclaim 10, wherein: detecting the condition indicative of the presence ofthe MRI scanner comprises detecting the condition indicative of thepresence of the MRI scanner in response to detecting a magnetic fieldhaving a strength that is greater than or equal to a threshold strength;and subsequently determining the type of the MRI scanner comprisesdetermining the type of the MRI scanner based on a frequency of detectedRF energy.
 18. The method of claim 10, wherein the default exposureoperating mode is an exposure operating mode corresponding to a firsttype of MRI scanner and the second exposure operating corresponds to asecond type of MRI scanner different than the first MRI scanner.
 19. Themethod of claim 18, wherein the first type of MRI scanner is a 1.5 TeslaMRI scanner and the second type of MRI scanner is a 3.0 Tesla MRIscanner.
 20. An implantable medical device comprising: means for storinga plurality of exposure operating modes, wherein each of the pluralityof exposure operating modes corresponds to pacing parameters for useduring exposure to a particular type of MRI scanner; means for detectinga condition indicative of a presence of a magnetic resonance imaging(MRI) scanner; means for determining a type of MRI scanner in responseto detecting the condition; means for selecting one of the plurality ofexposure operating modes based on the determination of the type of MRIscanner; and means for configuring the implantable medical device tooperate in accordance with the operating parameters of the selectedexposure operating mode.
 21. The device of claim 20, wherein thedetecting means detect the condition indicative of the presence of theMRI scanner in response to one of detecting a static magnetic field thatexceeds a static field strength threshold, detecting one or moregradient magnetic fields that exceed a gradient field strength thresholdand detecting one or more radio frequency (RF) signals of a particularfrequency.
 22. The device of claim 20, wherein the determining meansdetermine the type of MRI scanner comprises determining the type of MRIscanner based on the detected condition.
 23. The device of claim 22,wherein the detecting means detect the condition based on a magnitude ofa magnetic field to which the implantable medical device is exposed; andthe determining means determine the type of MRI scanner based on themagnitude of the magnetic field to which the implantable medical deviceis exposed.
 24. The device of claim 20, wherein the detected conditioncomprises a first condition, the device further comprising: means fordetecting a second condition; and wherein the determining meansdetermine the type of MRI scanner based on the second detectedcondition.
 25. The device of claim 24, wherein the determining meansdetermines a frequency of RF energy to which the implantable medicaldevice is exposed and determines the type of MRI scanner based on thedetermined frequency of the RF energy.
 26. The device of claim 20,wherein the configuring means configures a filter to attenuate afrequency associated with the determined type of MRI scanner.
 27. Thedevice of claim 20, wherein the configuring means configures theimplantable medical device to operate in accordance with a defaultexposure operating mode in response to detecting the presence of the MRIscanner and configures the implantable medical device to operate inaccordance with the operating parameters corresponding to the particulartype of MRI scanner in response to detecting the type of MRI scanner.28. The device of claim 20, wherein the pacing parameters include atleast one of a pacing amplitude, pacing pulse width, pacing mode, andpacing rate.